1. Field of the Invention
The invention relates to a filter device for fluids, including a filter case containing at least one filter inlet and one filter outlet and one filter arranged in between. The device includes a duct for by-passing a portion of the filter, and a valve for by-passing the entire filter. The invention also relates to a method for filtering fluids through a filter, including the steps of introducing a fluid, filtering the fluid until the pressure across the filter reaches a first limit, by-passing a portion of the filter while continuing filtering the fluid, and by-passing the filter entirely when the pressure across the filter reaches a second limit. The first and second limit may be the same or different.
2. Prior Art
Particles of various sizes and consistency which collect in liquid and gas media used for lubricating and/or cooling moving machine parts as a result of wear, corrosion, contamination and related condensates and emulsions, must be filtered out of the media to prevent damage to machines. Particles such as these cause damage to engines, pumps, controls, regulators, so that such systems age more quickly due to mechanical wear and corrosion. Even liquid media such as motor oil, transmission oil, hydraulic oil, transformer oil, petroleum and synthetic oils and mixtures, mineral oils, partially and completely biological oils or their mixtures, and completely synthetic oils cause wear due to such particles and become contaminated more quickly. If the particles and contaminants are not filtered out, the systems can experience clogging or adhesive lock since the liquid media, such as the diverse oils specified above, can thicken due to accumulation of particles and/or the formation of an emulsion, i.e. its viscosity increases and, hence, a high degree of friction is created in lubricating slots, along crankshafts and at other moving machine parts. If soft particles as large as approx. 30 μm are pulverized, the number of particles, i.e. the particle density, increases, resulting in the pulverized particles severely lowering the air release property of the oils, which in turn results in an acceleration of the oxidative corrosion and cavitation of the machine parts due to the oxygen contained in the oil. Hence, for example, if the lubricating slot in a piston engine is not completely wetted or filled with oil, elliptic bulges are created which reduce engine performance and engine efficiency and lead to increased fuel and oil consumption as well as to increased exhaust emissions. Pumps in the hydraulic system are subject to the same negative effects as engines. In the case of slide-valve controls which regulate the feed rate, particles and contaminants can cause a rounding of the slide-valve rods, i.e. the result is what is known as a control deviation. The slide volume control then reacts less precisely and less sensitively.
The filter device in the circulatory system of the filtered liquid or gas media filters the particles, contaminants and water out of the media.
Because of the large discrepancy between the temperature in the engine's crankcase, roughly 260 to 280° C., and the ambient temperature, approximately 20° C., water vapor condenses out of the ambient air and enters the engine oil, in this manner. Water can also enter the motor oil if the cylinder head seals leak or burst. When the engine cools down, water collects in the oil pan and gets into the filter device when the engine is cold-started. The known filters generally only have a negligible water capacity; as they absorb water their materials quickly swell and are filled to capacity. The filter service life of known filters is approximately 500 hours. The service life of the media to be filtered, especially the oil service life, is also reduced by the short service life of the filters—if they are not changed at the same time as the filters.
DE 42 21 897 A1 discloses a filter device featuring one coarse filter and one fine filter, connected in parallel, for liquid or gas media, especially for hydraulic oil. A flow regulating valve, connected upstream from the fine filter, limits the volumetric flow of the liquid or gas medium through the fine filter to a preset value. The coarse filter is equipped with a bypass valve. One part of the volumetric flow of the filtered medium is fed directly through the coarse filter, while another part of the volumetric flow is fed through the flow regulation valve and then through the fine filter. The volumetric flows filtered in the coarse and fine filters are subsequently joined together at one duct outlet. Regulating the volumetric flow to a preset value protects the fine filter from pressure peaks in the medium. If the coarse filter is characterized by a high degree of contamination and if, due to this, it becomes impenetrable to the filtered medium, or if the medium to be filtered has a high degree of viscosity, such as cold hydraulic oil, so that it cannot pass through the coarse filter and the fine filter, the volumetric flow is fed unfiltered through the bypass valve. This avoids any restriction or interruption in the circulation of the volumetric flow of the filtered medium.
In DE 196 44 647 A1 a filter for fluids is described featuring a substantially pot-shaped case in which a filter insert is arranged consisting of a filter element folded in a zigzag shape and face end discs. The filter case has a fastening flange and a lid which is connected by means of a screw or bayonet connection to the fastening flange. A single replaceable filter insert is arranged in the filter case.